You definitely have a form of sciatica. You probably hurt your back or tweaked it at one time and now it's causing you problems. What happens is that the muscles in your core (hips, thighs, buttocks, lower back) spasm and get knotted. When this happens they pull your pelvis and spine out of alignment. What I did to stop my problems is to start doing inversion therapy or hang upside down with gravity boots. As you invert the muscles of your abs are stretched and the knots are broken up. As this happens they release their grip on the muscles in your hips and thighs. As they loosen they will release their grip on the muscles in your lower back. As this happens they in turn release their grip on your pelvis and lower spine and allow it to go back into alignment naturally with gravity. When your spine and pelvis are out of alignment it effects the sciatic nerve and that's what's causing your pain. I guarantee if you try inversion therapy within a week or so your pain will be gone. Here's a good site to read about what I'm talking about. Hope this helps.